Vertically integrated MEMS structure with electronics in a hermetically sealed cavity

Abstract

A MEMS assembly having a MEMS subassembly sandwiched between and bonded to a cap and a base is provided. The MEMS subassembly includes at least one MEMS device element flexibly connected to the MEMS assembly. The vertical separation between the MEMS device element and an electrode on the base is lithographically defined. Precise control of this critical vertical gap dimension is thereby provided.

1. A vertically integrated microelectromechanical (MEMS) assembly comprising:
 a MEMS subassembly including a substantially planar frame and at least one MEMS device element within the frame and flexibly connected to the assembly; 
 a cap bonded to the frame with a first bond, the first bond being substantially parallel to the frame; and 
 a base bonded to a surface of the frame facing away from the cap with a second bond; 
 wherein a gap between an electrode on the base and the MEMS device element is defined by a lithographic feature on the frame; 
 whereby precise control of the gap is provided and the at least one MEMS device element is enclosed within a cavity. 
 
   
   
     2. The MEMS assembly of  claim 1 , wherein the gap between the electrode and the MEMS device element is not equal to a height of the lithographic feature on the frame. 
   
   
     3. The MEMS assembly of  claim 1 , wherein the gap between the electrode and the MEMS device element is equal to a height of the lithographic feature on the frame. 
   
   
     4. The MEMS assembly of  claim 1 , wherein the gap is in a range from about 1 micron to about 10 microns. 
   
   
     5. The MEMS assembly of  claim 1 , wherein the gap is less than about 2 microns. 
   
   
     6. The MEMS assembly of  claim 1 , further comprising an electrostatic actuator including the electrode for moving the MEMS device element. 
   
   
     7. The MEMS assembly of  claim 1 , wherein the cap comprises an electrically insulating layer bonded to the frame. 
   
   
     8. The MEMS assembly of  claim 1 , wherein the cap includes a recess permitting motion of the MEMS device element. 
   
   
     9. The MEMS assembly of  claim 1 , wherein the cavity is hermetically sealed. 
   
   
     10. The MEMS assembly of  claim 9 , wherein a gas pressure within the cavity is other than atmospheric pressure. 
   
   
     11. The MEMS assembly of  claim 9 , wherein a gas within the cavity comprises dry nitrogen, dry air, He, or Ar. 
   
   
     12. The MEMS assembly of  claim 1 , wherein the base includes a recess permitting motion of the MEMS device element. 
   
   
     13. The MEMS assembly of  claim 1 , wherein the base further comprises circuitry electrically connected to the MEMS subassembly. 
   
   
     14. The MEMS assembly of  claim 13 , wherein the circuitry comprises CMOS circuitry. 
   
   
     15. The MEMS assembly of  claim 13 , wherein the circuitry comprises multilayer metallization, whereby electrical feed through from within the cavity to outside the cavity is provided. 
   
   
     16. The MEMS assembly of  claim 13 , wherein the second bond is an AlGe bond between Ge on the frame and Al on the base, and wherein the Al is provided by the same processing that provides the circuitry. 
   
   
     17. The MEMS assembly of  claim 13 , further comprising selective electrical contacts between the frame and the circuitry. 
   
   
     18. A MEMS device comprising a plurality of MEMS assemblies according to  claim 1  having a common cap and a common base.